Organic synthesis by condensation reactions resulting in the loss of a molecule of water or of ammonia is well known in the art. Certain of such reactions are generally effected in the presence of acidic catalysts. An important area in which such acid catalysis has been employed is in cyclization reactions as in the synthesis of triethylenediamine and its C-substituted homologues. The catalysts are typically solid products of the Lewis acid type.
One group of catalysts which have been found to be effective for acid catalyzed organic condensation reactions such as those used to produce triethylenediamine (also referred to herein as TEDA) are phosphate catalysts. The following patents provide examples of such phosphate catalysts.
U.S. Pat. No. 3,297,701 (Brader et al., 1967) discloses the use of metal phosphate catalysts such as aluminum phosphate, calcium phosphate and cobalt phosphate, for synthesis of TEDA and C-substituted TEDA from piperazines or alkanolamines.
U.S. Pat. No. 4,405,784, U.S. Pat. No. 4,514,567, and U.S. Pat. No. 4,521,600 (Wells et al, 1983-1985) disclose the use of strontium monohydrogen phosphate (SrHPO.sub.4), strontium pyrophosphate (Sr.sub.2 P.sub.2 O.sub.7), strontium dihydrogen phosphate (Sr(H.sub.2 PO.sub.4).sub.2), the pyrophosphate, monohydrogen phosphate and dihydrogen phosphate of copper, magnesium, calcium, barium, zinc, aluminum, lanthanum, cobalt, nickel, cerium and neodymium, and mixtures thereof, as effective catalysts for organic condensation reactions especially the reaction to form TEDA. The catalysts are made by reacting a soluble salt of one of the metals with the mono- or diphosphate of an alkali metal or ammonium. The pH of the reaction mixture is adjusted to 5.+-.3 in order to precipitate out the mono- or dihydrogen phosphate of the metal.
U.S. Pat. No. 4,757,143 (Vanderpool et al, 1988) discloses the conversion of cyclic and acyclic hydroxyethyl ethylenepolyamines to TEDA using a catalyst composed of zirconia or titania to which from 0.5 to about 7 wt % of phosphorous has been thermally chemically bonded in the form of phosphate linkages.
U.S. Pat. No. 5,037,838 (Zimmerman et al, 1991) discloses the conversion of N-hydroxyethyl piperazine to TEDA using a titania-supported tungstopyrophosphate catalyst.